This invention relates to an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid medium, to electrosurgical apparatus including such an instrument, and to an electrode unit for use in such an instrument.
Endoscopic electrosurgery is useful for treating tissue in cavities of the body, and is normally performed in the presence of a distension medium. When the distension medium is a liquid, this is commonly referred to as underwater electrosurgery, this term denoting electrosurgery in which living tissue is treated using an electrosurgical instrument with a treatment electrode or electrodes immersed in liquid at the operation site. A gaseous medium is commonly employed when Endoscopic surgery is performed in a distensible body cavity of larger potential volume in which a liquid medium would be unsuitable, as is often the case in laparoscopic or gastroenterological surgery.
Underwater surgery is commonly performed using endoscopic techniques, in which the endoscope itself may provide a conduit (commonly referred to as a working channel) for the passage of an electrode. Alternatively, the endoscope may be specifically adapted (as in a resectoscope) to include means for mounting an electrode. or the electrode may be introduced into a body cavity via a separate access means at an angle with respect to the endoscopexe2x80x94a technique commonly referred to as triangulation. These variations in technique can be subdivided by surgical speciality, where one or other of the techniques has particular advantages given the access route to the specific body cavity. Endoscopes with integral working channels, or those characterised as resectoscopes are generally employed when the body cavity may be accessed through a natural body openingxe2x80x94such as the cervical canal to access the endometrial cavity of the uterus, or the urethra to access the prostate gland and the bladder. Endoscopes specifically designed for use in the endometrial cavity are referred to as hysteroscopes, and those designed for use in the urinary tract include cystoscopes, urethroscopes and resectoscopes. The procedures of transurethal resection or vaporisation of the prostate gland are known as TURP and EVAP respectively. When there is no natural body opening through which an endoscope may be passed, the technique of triangulation is commonly employed. Triangulation is commonly used during underwater endoscopic surgery on joint cavities such as the knee and the shoulder. The endoscope used in these procedures is commonly referred to as an arthroscope.
Electrosurgery is usually carried out using either a monopolar instrument or a bipolar instrument. With monopolar electrosurgery, an active electrode is used in the operating region, and a conductive return plate is secured to the patient""s skin. With this arrangement, current passes from the active electrode through the patient""s tissues to the external return plate. Since the patient represents a significant portion of the circuit, input power levels have to be high (typically 150 to 250 watts). to compensate for the resistive current limiting of the patient""s tissues and, in the case of underwater electrosurgery, power losses due to the fluid medium which is rendered partially conductive by the presence of blood or other body fluids. Using high power with a monopolar arrangement is also hazardous, due to the tissue heating that occurs at the return plate. which can cause severe skin burns. There is also the risk of capacitive coupling between the instrument and patient tissues at the entry point into the body cavity.
With bipolar electrosurgery, a pair of electrodes (an active electrode and a return electrode) are used together at the tissue application site. Thus arrangement has advantages from the safety standpoint, due to the relative proximity of the two electrodes so that radio frequency currents are limited to the region between the electrodes. However, the depth of effect is directly related to the distance between the two electrodes; and, in applications requiring very small electrodes, the inter-electrode spacing becomes very small, thereby limiting tissue effect and the output power spacing the electrodes further apart would often obscure vision of the application site, and would require a modification in surgical technique to ensure direct contact of both electrodes with the tissue.
There are a number of variations to the basic design of the bipolar probe. For example, U.S. Pat. No. 4,706,667 describes one of the fundamentals of the design, namely that the ratio of the contact areas of the return electrode and of the active electrode is greater than 7:1 and smaller than 20:1 for cutting purposes. This range relates only to cutting electrode configurations. When a bipolar instrument is used for desiccation or coagulation, the ratio of the contact areas of the two electrodes may be reduced to approximately 1.1 to avoid differential electrical stresses occurring at the contact between the tissue and the electrode.
The electrical junction between the return electrode and tissue can be supported by wetting of the tissue by a conductive solution such as normal saline. This ensures that the surgical effect is limited to the needle or active electrode, with the electric circuit between the two electrodes beings completed by the tissue. One of the obvious limitations with the design is that the needle must be completively buried in the tissue to enable the return electrode to complete the circuit. Another problem is one of the orientation, even a relatively small change in application angle from the ideal perpendicular contact with respect to the tissue surface, will change the contact area ratio, so that a surgical effect can occur in the tissue in contact with the return electrode.
Cavity distension provides space for gaining access to the operation site, to improve visualisation and to allow for manipulation of instruments. In low volume body cavities, particularly where it is desirable to distend the cavity under higher pressure liquid rather than gas is more commonly used due to better optical characteristics, and because it washes blood away from the operative site.
Conventional underwater electrosurgery has been performed using a non-conductive liquid (such as 1.5% glycine) as an irrigant, or as a distension medium to eliminate electrical conduction losses. Glycine is used in isotonic concentrations to prevent osmotic changes in the blood when intra-vascular absorption occurs. In the course of an operation, veins may be severed, with resultant infusion of the liquid into the circulation, which could cause, among other things, a dilution of serum sodium which can lead to a condition known as water intoxication.
The applicants have found that it is possible to use a conductive liquid medium, such as normal saline, in underwater endoscopic electrosurgery in place of non-conductive, electrolyte-free solutions. Normal saline is the preferred distension medium in underwater endoscopic surgery when electrosurgery is not contemplated. or a non-electrical tissue effect such as laser treatment is being used. Although normal saline (0.9% w/v: 150 mmol/L) has an electrical conductivity somewhat greater than that of most body tissue, it has the advantage that displacement by absorption or extravasation from the operative site produces little physiological effect, and the so-called water intoxication effects of non-conductive, electrolyte-free solutions are avoided.
Carbon dioxide is the preferred gaseous distension medium, primarily because of its non-toxic nature and high water solubility.
In endoscopic procedures in which the distension medium is a gas, the applicants have found that it is possible to use an electrically-conductive gas (such as argon) in place of carbon dioxide. Argon is conductive when excited into a discharge state, and has been employed in both endoscopic and conventional monopolar electrosurgery as a method of increasing the distance between the tissue and the instrument, by providing a conductive path between the two when high voltage electrosurgical outputs such as spray or fulgurate are being used. The high voltages used in this application result in a very low penetration of the electrosurgical effect into the tissue, making the technique only suitable to control bleeding from multiple small blood vessels. This allows the surgeon to staunch bleeding from multiple sites in a surgical sites in a surgical wound using a rapid xe2x80x9cpaintingxe2x80x9d technique, rather than applying electrosurgery to each individual bleeding site. The argon gas is delivered through a hollow surgical instrument, and passes over the monopolar electrode exposed at the tip of the instrument as a stream. This produces a region at the operative site which is rich in argon, and which contributes to the distension of the body cavity. High voltage monopolar electrosurgical outputs are undesirable in endoscopic surgery, because of the risks of damaging structures outside the field of vision, by either capacitive or direct coupling to a portion of the instrument remote from the operative site often outside the field of vision of the operator.
The applicants have developed a bipolar instrument suitable for underwater electrosurgery using a conductive liquid or gaseous medium. This electrosurgical instrument for the treatment of tissue in the presence of a fluid medium comprises an instrument body having a handpiece and an instrument shaft and an electrode assembly, at one end of the shaft. The electrode assembly comprises a tissue treatment (active) electrode which is exposed at the extreme distal end of the instrument, and a return electrode which is electrically insulated from the tissue treatment electrode and has a fluid contact surface spaced proximally from the exposed part of the tissue treatment electrode. In use of the instrument, the tissue treatment electrode is applied to the tissue to be treated whilst the return electrode. being spaced proximally from the exposed part of the tissue treatment electrode, is normally spaced from the tissue and serves to complete an electrosurgical current loop from the tissue treatment electrode through the tissue and the fluid medium. This electrosurgical instrument is described in the specification of our European Patent Application 96918786.1
The electrode structure of this instrument, in combination with an electrically-conductive fluid medium, largely avoids the problems experienced with monopolar or bipolar electrosurgery. In particular, input power levels arc much lower than those generally necessary with a monopolar arrangement (typically 100 watts). Moreover, because of the relatively large spacing between its electrodes, an improved depth of effect is obtained compared with conventional bipolar arrangements.
The specification of our International Patent Application GB96/01472 describes an irritated bipolar electrosurgical instrument that can be used in open air or gas-filled environments This instrument includes an internal channel for feeding electrically-conductive fluid (typically saline) to the exposed end of a tissue treatment electrode so as to provide a conductive fluid path that completes an electrical circuit to a return electrode when the instrument is in use. This instrument also includes an internal channel for removing fluid from the region of the exposed end of the tissue treatment electrode. When the fluid is a liquid, such as saline, the presence of that liquid can cause collateral tissue damage, so its removal is desirable. This type of instrument is intended primarily for use in open air or Las-filled environments, and is not suitable for use with electrosurgical procedures which require distension of a body cavity.
However, where the volume of a body cavity is smallxe2x80x94for example in arthroscope surgery where even the large joints, such as the knee, may only accommodate 50-60 ml of irrigation fluidxe2x80x94the following problems may occur, namely:
(i) Heated fluid in the immediate vicinity of the tissue contact electrode can cause collateral tissue damage;
(ii) The products of the tissue vaporized by the tissue contact electrode can cause visualisation problems; and
(iii) Soft tissue present in anoint space tends to move about, making it difficult to apply the active electrode to vaporise such tissue.
An arthroscope electrode may be characterised as short (100 to 140 mm), and rigid with a working diameter up to 5 mm. It can be introduced through a stab incision into a joint cavity (with or without a cannula) using the triangulation technique. Such an electrode is operated with a motion which moves the electrode between the 9 O""Clock and 3 O""Clock positions on the arthroscopic image As a result, the tissue to be treated is usually approached at a shallow working angle with respect to the axis of the electrode. An arthroscopic electrode thus needs to have an effect consistent with this angled approach to the tissue The tissue to be treated, such as meniscal cartilage, is commonly dense and of a high electrical impedance. An arthroscope electrode requires output power and voltage settings that reflect the type of tissue being treated, the size of electrode, and the fact that arthroscopists are seeking a speed of effect comparable to that of the mechanical shaver devices they currently employ, albeit with an electrode of smaller dimensions than a shaver blade for improved access.
The aim of the invention is to provide an Improved electrosurgical instrument of this type.
The present invention provides a electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid medium, the instrument comprising an instrument shaft. and an electrode assembly at one end of the shaft, the electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode having an exposed end for treating tissue, and the return electrode having a fluid contact surface which is spaced proximally from the tissue treatment electrode in such a manner as to define, in use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the return electrode, wherein the electrode assembly is provided with a plurality of apertures in the region of the tissue treatment electrode and distal to the return electrode, through which apertures vapour bubbles and/or particulate material can be aspirated from the region surrounding the tissue treatment electrode.
In a preferred embodiment, the instrument further comprises a pump for subjecting the distal end portion of the instrument shaft to a sub-atmospheric pressure thereby to aspirate, in use, vapour bubbles and/or particulate material through said apertures from the region surrounding the tissue treatment electrode.
Advantageously, the pump is activated cyclically whereby matter is aspirated in a pulsed fashion. The pump may additionally or alternatively be activated only when the tissue treatment electrode is powered for tissue vaporisation.
Preferably, the instrument further comprises an RF generator having a bipolar output connected to the tissue treatment electrode and the return electrode. In this case, the pump may be controlled in dependence upon the voltage output characteristics of the RF generator. In this way, the flow of vapour bubbles and/or aspirated particulate material is balanced to the voltage output characteristics of the RF generator to prevent excessive cooling of the tissue treatment electrode and a resultant increase in the vaporisation power threshold. The return electrode is spaced from the tissue treatment electrode so that, in use, it does not contact the tissue to be treated, and so that the electrical circuit is always completed by the conductive fluid, and not simply by arcing between the electrodes. Indeed, the arrangement is such that arcing between adjacent parts of the electrode assembly is avoided, thereby ensuring that the tissue treatment electrode can become enveloped in a vapour pocket so that tissue entering the vapour pocket becomes the preferred path for current to flow back to the return electrode via the conductive fluid.
The electrosurgical instrument of the invention is useful for dissection, resection, vaporisation, desiccation and coagulation of tissue, as well as for combinations of these functions. It has a particular application in arthroscopic surgery as it pertains to endoscopic and percutaneous procedures performed on joints of the body including, but not limited to, such techniques as they apply to the spine and other non-synovial joints. Arthroscopic operative procedures may include: partial or complete meniscectomy of the knee joint including meniscal cystectomy, lateral retinacular release of the knee joint, removal of anterior and posterior cruciate ligaments or remnants thereof, labral tear resection, acromioplasty, bursectomy and subacromial decompression of the shoulder joint; anterior release of the temperomandibular joint; synovectomy, cartilage debricement, chondroplasty, division of intra-articular adhesions, fracture and tendon debricement as applied to any of the synovial joints of the body, inducing thermal shrinkage of joint capsules as a treatment for recurrent dislocation, subluxation or repetitive stress injury to any articulated joint of the body; discectomy either in the treatment of a disc prolapse or as part of a spinal fusion via a posterior or anterior approach to the cervical, thoracic and lumbar spine or any other fibrous joint for similar purposes; excision of diseased tissue; and haemostasis.
The instrument of the invention is also useful for dissection, resection, vaporisation, desiccation and coagulation of tissue, as well as combinations of these functions, with particular application in urological endoscopic (urethroscopy, cystoscopy, ureteroscopy and nephroscopy) and percutaneous surgery. Urological procedures may include: electro-vaporisation of the prostate gland (EVAP) and other variants of the procedure commonly referred to as transurethal resection of the prostate (TURP) including but not limited to, interstitial ablation of the prostate gland by a percutaneous or perurethral route whether performed for benign or malignant disease; transurethal or percutaneous resection of urinary tract tumours as they may arise as primary or secondary neoplasms, and further as they may arise anywhere in the urological tract from the calyces of the kidney to the external urethral meatus; division of strictures as they may arise at the pelviureteric junction (PUJ), ureter, ureteral orifice, bladder neck or urethra; correction of ureterocoele, shrinkage of bladder diverticular, cystoplasty procedures as they pertain to corrections of voiding dysfunction; thermally induced shrinkage of the pelvic floor as a corrective treatment for bladder neck descent, excision of diseased tissue, and haemostasis.
Surgical procedures using the electrosurgical instrument of the invention may also include introducing the electrode assembly to the surgical site, whether through an artificial conduit (a cannula) or a natural conduit, which may be in an anatomical body cavity or space, or one created surgically. The cavity or space may be distended during the procedure using a fluid, or may be naturally held open by anatomical structures. The surgical site may be bathed in a continuous flow of conductive fluid such as saline solution either to fill and distend the cavity, or to create a locally-irrigated environment around the tip of the electrode assembly in a gas filled cavity. The irrigating fluid may be aspirated from the surgical site to remove products created by application of the RF energy, tissue debris or blood. The procedures may include simultaneous viewing of the site via an endoscope, or using an indirect visualisation means. An irrigated bipolar electrosurgical instrument is described in the specification of our International Patent Application GB96/01471
Advantageously, the exposed end of the tissue treatment electrode extends laterally through a cut-out provided in the insulation member at the distal end portion of the instrument, the fluid contact surface of the return electrode overlying the insulation member in the region of the cut-out.
In a preferred embodiment, a single coiled filament constitutes the tissue treatment electrode, and said apertures are formed in the insulation member, the apertures being positioned around, and adjacent to, the tissue treatment electrode. Preferably, the filament has a diameter lying within the range of from 0.05 mm to 1.0 mm.
Alternatively, an apertured plate constitutes the tissue treatment electrode, the apertures of the plate constituting the apertures through which vapour bubbles and/or particulate material can be aspirated. The outer surface of said plate may be formed with recesses adjacent to the apertures. The recesses trap vapour pockets and so reduce the vaporisation power threshold of the instrument.
The tissue treatment electrode may be made of tungsten or of an alloy of tungsten or platinum.
Preferably, the instrument further comprises a tube positioned within the instrument shaft for connecting said apertures to the pump. The tube may be a multi-lumen tube, in which case it defines a plurality of channels, the diameter of each of said channels being at least equal to the diameter of the apertures in the region of the tissue treatment electrode. Alternatively, the instrument further comprises a filter at the distal end of the tube.
The invention also provides an electrode unit for an electrosurgical instrument for the treatment of tissue in the presence of an electrical-conductive fluid medium, the electrode unit comprising a shaft having at one end means for connection to an instrument handpiece. and, mounted on the other end of the shaft. an electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode having an exposed end for treating tissue, and the return electrode having a fluid contact surface which is spaced from the tissue treatment electrode in such a manner as to define, in use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the return electrode, wherein the electrode assembly is provided with a plurality of apertures in the region of the tissue treatment electrode, through which apertures vapour bubbles and/or particulate material can be aspirated from the region surrounding the tissue treatment electrode.
The invention further provides electrosurgical apparatus comprising a radio frequency generator and an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid medium, the instrument comprising an instrument shaft, and an electrode assembly at one end of the shaft, the electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode having an exposed end for treating tissue, and the return electrode having a fluid contact surface which is spaced from the tissue treatment electrode in such a manner as to define, in use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the return electrode, and the radio frequency generator having a bipolar output connected to the electrodes, wherein the electrode assembly is provided with a plurality of apertures in the region of the tissue treatment electrode, through which apertures vapour bubbles and/or particulate material can be aspirated from the region surrounding the tissue treatment electrode.